Freshwater Conditions Research Articles

Quaternary non-marine ostracods of Runtuyoc lake, northern Argentina: New taxonomic descriptions and the implication for Holocene paleoenvironment

We performed an ostracod taxonomic analysis on samples from a shallow lake (Runtuyoc Lake) in north-western Argentina in order to contribute to the understanding of the evolution of this water body through the last 5000 years. The ostracod assemblages consist of 15 species, two species exclusively from modern samples (Herpetocypris helenae and Chlamydotheca incisa), 8 exclusively from Quaternary samples (Limnocythere jujunensis sp. nov., L. titicaca, L. alexanderi, L. aff. staplini, Cyprideis salebrosa, Penthesilenula incae, Cypridopsis vidua, Sarscypridopsis aculeata) and 5 from both, modern and Quaternary samples (Ilyocypris ramirezi, Potamocypris smaragdina, Heterocypris incongruens, Heterocypris similis, Candona sp.). The lake is located in the Miraflores river course and is characterized nowadays by freshwater conditions, but a saline past is evident as it went through different periods of desiccation. From 5500 to 3000 cal a BP, the lake was absent, probably related to extreme dry conditions. Then, water inputs into the lake produced a saline shallow lake until to reach modern setting as a freshwater body basin. Runtuyoc lake records, supports the regional environmental trending change for the Argentinian northwest, with wetter conditions in the early and late Holocene, and arid for the middle Holocene at least from 5500 to 3000/2500 cal a BP.

Multi proxy analysis for reconstructing the late Holocene evolution of a Mediterranean Coastal Lagoon: Environmental variables within foraminiferal assemblages

This study reconstructs the evolution of foraminiferal assemblages and the environmental variables (type of substrate, content in calcium carbonate and content in organic matter) in the Valencia lagoon (western Mediterranean) in response to changes in the late Holocene. In this area of low tidal range, several multiproxy analyses were carried out to determine which environmental variables influence the distribution of the fossil assemblage, and its association with global, regional or local climatic phenomena. The statistical results show that in environments with higher exposure to marine conditions, the calcium carbonate content is the dominant factor, whereas in more restricted environments the type of substrate (grain size) is determinant. The micropaleontological content reveals the evolution from a saline paleoenvironment with a clear marine influence towards the hyposaline or freshwater conditions, recorded at the top.Three phases were identified in the evolution of this area from 2800 cal yr BP to the present. A brackish lagoon with marine connection at the base, followed by a deposit of brackish lagoon (1232 ± 74 cal yr BP − 791 ± 104 cal yr BP), culminating in a brackish marsh (791 ± 104 cal yr BP to present), interpreted as the definitive closure process of the lagoon, favored by the coastal progradation processes related with an extraordinary input of sediments. These findings reflect the climatic variability of the Medieval Climate Optimum (MCO) (1.05 and 0.65 kcal BP) and the migration of the river Turia mouth, which favored the coastal progradation processes. The flood events registered at this phase, may have coincided with changes in the landscape and greater anthropic influence at the end of the LIA, 150 cal yr BP. Coastal processes are mainly responsible for the evolution of this area during phase I, while the influence of fluvial processes is significant towards the top, especially in phase III.

Direct and Carryover Effects of Freshwater, Marine and Fish Conditions on Juvenile, Ocean, and Adult Survival of Snake River Chinook Salmon

Direct and Carryover Effects of Freshwater, Marine and Fish Conditions on Juvenile, Ocean, and Adult Survival of Snake River Chinook Salmon

Plant fossils from the Wealden facies (Lower Cretaceous, Berriasian) of Tecklenburg, Westphalia, Germany

While the Early Cretaceous flora of the English Wealden has been extensively revised in the last decades, the flora from the German Wealden is still in need of thorough revision. One major account on a flora from Duingen in the eastern Lower Saxony Basin (Niedersächsisches Becken) has been published a couple of years ago, but was covering freshly collected fossil material only. Here, a small flora from the southern margin of the Lower Saxony Basin is reported coming from Brochter-beck, a district of Tecklenburg, at the northern slopes of the Teutoburger Wald mountain range in Westphalia, Germany. The flora shows a slightly different composition compared to those of the 'classical' German Wealden: it is also characterised by remains of several delicate filmy ferns and cupressoid (taxodiaceous) conifers, but it is dominated by the presence of leaves of Nilssonia schaumburgensis, while other cycadophytes such as cycads and bennettites are entirely absent. One leaf reminiscent of a Ginkgo species was found as well. The relatively fine-grained sandstones of the rocks comprising the flora at Brochterbeck reflect a terrestrial deposit of the Wealden facies, which was deposited under deltaic freshwater conditions in brackish–limnic conditions in a humid, subtropical climate.

Life on the edge: Compensatory growth and feeding rates at environmental extremes mediates potential ecosystem engineering by an invasive bivalve

Invasive non-native species (INNS) with marine or brackish origins have become increasingly common occupying freshwater habitats. The transition of INNS from marine or brackish water into physiologically stressful freshwater environments may be facilitated by compensatory growth and elevated feeding rates. In this study, we investigate the capacity of the Gulf wedge clam (Rangia cuneata), a brackish NNS that is spreading quickly across European waterways, to survive in freshwater conditions and consider its resultant impacts as an ecosystem engineer. To investigate the performance of R. cuneata under freshwater conditions, we compared the population structure, the physiological condition, and the growth of R. cuneata collected from its distributional limits in Great Britain. Feeding rate of R. cuneata was quantified by conducting a reciprocal transfer experiment with a two-way factorial design on individuals obtained from the freshwater and saline extremes. R. cuneata density was almost 10-fold higher at its most saline distributional limit (213 individual m−2, 3.1‰) compared to its most freshwater limit (22 individuals m−2, 1.2‰). The impaired physiological condition (18.7% lower relative soft tissue mass and 26.4% lower shell mass) and the lack of juvenile individuals also suggests that the R. cuneata inhabiting the freshwater extreme may not be able to maintain a persistent population over the long term. Although R. cuneata at its freshwater extreme were under stress, the per capita impacts caused by these individuals were not weakened at the suboptimal conditions, evidenced by their elevated growth and over four times as high relative clearance rate (0.28 L−1 g−1 h−1) compared to those from the saline limit (0.06 L−1 g−1 h−1). This study demonstrates that under suboptimal conditions, the physiological responses of INNS may result in elevated per capita effects which may lead to unexpected or under-estimated impacts on recipient ecosystems.

Characterisation of selected micro-estuaries and micro-outlets in South Africa using microalgal, zooplanktonic and macrozoobenthic assemblages

South Africa has approximately 200 micro-estuaries and micro-outlets along its more than 3 000 km of coastline. Many of these microsystems (i.e. micro-outlets and micro-estuaries) share some characteristics with temporarily open/closed estuaries, but differ in that they are supplied by localised catchments with limited supply of freshwater and less connectivity to the marine environment. Between 2015 and 2016 we investigated whether micro-outlets and micro-estuaries can be differentiated from each other and other estuaries based on physico-chemical properties, microalgal dynamics, as well as species diversity and composition of invertebrate communities. The micro-outlets were dominated by oligohaline or freshwater conditions, whereas micro-estuaries were mostly mesohaline. Microalgal biomass in both system types was influenced by temperature, nutrient concentration and light availability. The micro-estuaries had a higher microalgal biomass than the micro-outlets. Chironomidae and Ephemeroptera numerically dominated benthic macroinvertebrate micro-outlet communities, whereas Amphipoda and Mysida were most dominant in micro-estuaries. Calanoid copepods dominated zooplankton assemblages in micro-estuaries and macroinvertebrate larvae in micro-outlets. In addition, the zooplankton densities were significantly higher (p < 0.05) in micro-estuaries compared with micro-outlets. Study results confirm that there are major differences between the biota in the two microsystem types, accordingly making biotic assemblages, together with physico-chemical parameters, a viable tool for differentiating between micro-estuaries and micro-outlets.

Are there any true marine Chlorella species? Molecular phylogenetic assessment and ecology of marine Chlorella-like organisms, including a description of Droopiella gen. nov.

Green algal species of spherical cell shape are generally considered to belong to the genus Chlorella, which are mostly freshwater or terrestrial organisms. Phylogenetic studies have shown that this genus is polyphyletic and belongs to different classes. However, until now, only freshwater or terrestrial strains have been studied. Here we investigated 11 strains of ‘marine’ Chlorella deposited in public culture collections, which we studied using an integrative approach. These strains were largely isolated from marine rock pools and brackish estuaries. SSU and ITS regions of the nuclear encoded ribosomal DNA were sequenced, ribosomal secondary structures were analysed and cell morphology, salinity tolerance and reproduction were examined. Our results showed that the marine strains are also of polyphyletic origin. Surprisingly, three marine isolates belong to Chlorella vulgaris according to the phylogenetic analyses, but showed a high phenotypic plasticity. Whereas these strains showed the typical morphology of C. vulgaris under freshwater conditions, they increased the cell shape and formed cell packages under marine conditions. In contrast, the other investigated strains showed no changes after changing the media. Two of the investigated strains belong to the genus Chloroidium, and those remaining represent a new genus, Droopiella.

Lacustrine environmental evolution and implications on source rock deposition in the Upper Cretaceous-Paleocene of the South Yellow Sea Basin, offshore eastern China

Lacustrine source rocks are well developed within the Upper Cretaceous-Paleocene in the South Yellow Sea Basin (SYSB) in offshore eastern China. Understanding the deposition of these source rocks could provide critical information for hydrocarbon exploration in the SYSB, as well as reveal the paleoenvironment across the Cretaceous/Paleogene boundary in eastern China. This study investigates the lacustrine environmental evolution during the Upper Cretaceous Taizhou Formation (K2t) to Paleocene Funing Formation (E1f) within the SYSB and its implications on source rock deposition based on core observation combined with organic geochemical indicators. Multiple maturity parameters (vitrinite reflectance, Tmax and biomarker isomerization ratios) reveal that the organic matter (OM) has reached early oil window maturity. The OM of source rocks is dominated by kerogen Type II-III (liptinite and vitrinite). Anoxic, saline-brackish deep to semi-deep lacustrine environments prevailed during the deposition of K2t2 (second member of the K2t), E1f2 (second member of the E1f) and E1f4L (lower unit of fourth member of the E1f). The deposition of three intervals was influenced by marine incursion, as evidenced by geochemical and paleontological results. Low to moderate TOC contents (avg. 0.78 wt% to 1.91 wt%), which corresponds to low to moderate terrestrial OM input, are observed through three intervals. Abundant freshwater, together with high terrestrial OM flowed into the lacustrine environments during the deposition of E1f4U (upper unit of fourth member of the E1f), leading to dysoxic-oxic and freshwater conditions. High terrestrial OM input is probably the major controlling factor for relatively high TOC contents (avg. 2.49%) in the E1f4U. An evolution from balanced-fill to overfilled lake-type is observed in the Upper Cretaceous-Paleocene of SYSB, consistent with an evolution from semi-arid to humid paleoclimate conditions. The E1f4U and E1f2 source rocks exhibit fair to good potential, whereas poor to fair potential is present in the E1f4L and K2t2 source rocks. Compared with the Paleogene source rocks in onshore eastern China, the Upper Cretaceous-Paleocene source rocks in the SYSB probably hold good potential for generating commercial quantity of oil, although further study on hydrocarbon generation kinetics of source rocks and overall basin history are needed.

Pedogenic siderites fossilizing Ediacaran soil microorganisms on the Baltica paleocontinent

AbstractEdiacaran siderite-bearing sedimentary rocks from the western part of the East European craton exhibit features typical of redoximorphic paleosols, including pedogenic siderite (e.g., sphaerosiderite) with uniform and negative δ18O and highly variable δ13C values. The siderite precipitated in water-logged soils in a hot and humid climate, and represents a rare example of pedogenic siderite formed before the rise of vascular plants. Morphology of soil microorganisms was preserved in three dimensions due to the early siderite precipitation. These are mainly filamentous and tube-like threads, which might belong to cyanobacteria or fungi, and spherical structures resembling green algae. This microbial life fostered development of strongly reducing soils in tropical wetlands on the Baltica paleocontinent. The Ediacaran sediments of the western East European craton, traditionally regarded as marine, are reinterpreted as containing sections affected by freshwater conditions, documenting the presence of microbial life on the Ediacaran land.

Characterizing cesium sorption in freshwater settings using fluvial sediments and characteristic water chemistries

Cesium-137 (137Cs) is a persistent contaminant that poses a significant risk to human health and the environment. Understanding the fate and transport of 137Cs following a contamination incident is necessary for effective containment and remediation. In this study, we performed experiments to investigate how Cs+ sorption processes are affected by sediment type and varying water chemistries to better understand how Cs+ is transported in freshwater settings. Sediment was collected from various river deposits along the Susquehanna River adjacent to the Safety Light Corporation United States Environmental Protection Agency (US EPA) Superfund site (Bloomsburg, PA) and characterized prior to being used in batch reactor experiments with waters characteristic of different regions in the US (Central US and Northeast US) and with three different cation types (Mg2+, Na+, and K+) over a range of ionic strengths. Greater amounts of Cs+ sorption occurred with increasing sediment mud (silt and clay) content, although no major differences in sorption between the Central and Northeast US water types were observed. At an ionic strength (I) of 10 mM, K+ inhibited Cs+ sorption most effectively, followed by Mg2+, with Na+ having little effect on Cs+ sorption over the range of ionic strengths tested (I = 0.1, 1, and 10 mM). Our findings indicate that for the representative freshwater conditions tested here, sediment type (e.g., clay fraction) has a greater influence on Cs+ sorption processes than water chemistry. Additional reactions or processes occurring in relatively fresh water could buffer cation competition for sorption sites. Conducting experiments using site-specific sediment samples and water chemistries is useful for predicting Cs+ sorption and mobility in distinct environmental settings, particularly when the level of Cs+ contamination is high and if the waste or contaminated (or receiving) waters have a relatively high ionic strength.

Paleo-environmental Conditions, Paleoclimatic Significance and Effects of Weathering on Clay Deposits in the Lower Benue Trough, Nigeria. Mineralogical Approach

Combined methods for mineralogical identifications were used to characterise the clay deposits within the Lower Benue Trough of Nigeria to interpret paleo-environmental conditions, the paleoclimatic significance of the trough, and effects of weathering on the minerals as factors that favour its deposition/accumulation within the trough which host other important industrial minerals like coal, barite, limestone etc. Bulk-sample random-powder XRD data and data for clay fractions deposited onto zero-background quartz plates were measured. The samples contained kaolinite, vermiculite, and traces of smectite, and the non-clay phases included quartz, microcline, and muscovite. All samples were unaffected after glycolation, confirming the absence of significant smectite. Muscovite was characterized by the nature of its 10 Å basal peak with a width of &lt;0.10° 2θ, which was very sharp. DTA/TGA results support the presence of kaolinite, and the characteristic kaolinite O-H, Al-OH, Si-OH and SiO-Al FTIR bands also confirmed its presence. Vermicular and book-like morphologies were observed under the SEM, typical of kaolinitic clay from in situ alteration. High kaolinite abundance in these sediments is consistent with intense weathering of parent rocks rich in Al under wet/ tropical paleo-climatic conditions with fresh and/or brackish water conditions in a continental setting. The variety of observed morphologies suggests that the deposits suffered more of chemical weathering. The clay deposits in Lower Benue Trough are quartz-rich, kaolinitic and derived from the chemical weathering of Al-rich source rocks.

Evaluation of paired carbon isotopic signals from the Ediacaran Doushantuo phosphorites: Diagenetic or primary?

This study reports high-resolution C-isotopic data of carbonate carbon (δ13Ccarb) and organic carbon (δ13Corg) from the Ediacaran Doushantuo carbonate and phosphorite as well as from the underlying tillite of the Nantuo Formation from the Datang mine and Chuanyuandong sections. For the Nantuo tillite in the Datang section, the striking negative δ13Ccarb values ranging mostly from −10‰ to −16‰ with negative δ18O values down to −27.2‰ and clear covariance between δ13Ccarb and δ18O, suggest that nearly all of the primary C and O-isotopic compositions have been reset by meteoric diagenesis. The near complete modification of the primary isotopic signals may be due to frequent exposure to fresh water conditions during diagenesis and the lithification of porous tillite sediment. The extremely negative δ13Ccarb values down to −16.8‰ suggest the contribution of 12C-enriched dissolved inorganic carbonate which originated from the remineralization of organic carbon during burial diagenesis. These observations suggest that caution is needed when using tillite samples for paleoenvironmental reconstruction.The correlative lower phosphorite deposits from the Datang and Chuanyuandong sections show clear covariance between δ13Ccarb and δ18O, although the Chuanyuandong phosphorites have more negative values of δ13Ccarb and δ18O than the Datang section. Although most of the δ18O values of the lower phosphorites may have been altered by secondary diagenetic processes, the δ13Ccarb values of >−3.5‰ and the δ13Corg values of <−28.0‰ may represent the primary isotopic compositions of contemporaneous phosphate-rich seawater. In contrast, the upper phosphorites, characterized by δ13Ccarb values ranging from −0.9‰ to 1.7‰ with the δ18O values from −0.2‰ to −4.5‰ and the absence of covariance between δ13Ccarb and δ18O, may have recorded the primary isotopic signals of seawater from which the phosphorites were formed. It appears that the chemical composition of phosphate-rich seawater may have changed during the two phosphogenic events of the Ediacaran Doushantuo Formation.

Averting danger under the bridge: video confirms that adult small-toothed morays tolerate salinity before and during tidal influx

Safety considerations for researchers shape ecological research approaches in dangerous aquatic environments. A series of recent studies has demonstrated that the moray Gymnothorax polyuranodon (Family Muraenidae) occupies freshwater in the adult phase. However, its potential use of tidal habitat remains largely unexplored, due partly to the challenges of performing underwater research within estuarine crocodile territories. In September 2017, opportunistic snorkel-based observations revealed individuals of this species occupying lairs at an upper tidal creek site during low tide (under freshwater conditions). This provided an opportunity to tailor field-based measurements of the salinity tolerance of this species a fortnight later during a more substantial high tide. Specifically, remote underwater video, snorkel and above-water observations of morays, combined with salinity measurements, reveal that G. polyuranodon is capable of tolerating salinity of at least 14.4 for several hours and can inhabit salinity of 19 for a period of several minutes. This finding, when viewed in synergy with other relevant studies of G. polyuranodon, indicates that the species is either catadromous or amphidromous or capable of either strategy.

Development and Application of the Diffusive Gradients in Thin-Films Technique for Measuring Psychiatric Pharmaceuticals in Natural Waters

Psychiatric pharmaceuticals are widely distributed in the aquatic environment and have attracted recent attention due to their potential for environmental effects. A robust and reliable in situ passive sampling approach, the diffusive gradients in thin-films (DGT) technique, is developed here to measure 14 psychiatric pharmaceuticals. A new binding material, mixed-mode cation exchange resin (Poly-Sery MCX, 40 μm, CNW, Germany), was used for the first time in DGT and compared to XAD and HLB. Reliable elution efficiencies of the pharmaceuticals from the binding gels were obtained in methanol/ammonia, and diffusion coefficients for all the compounds were determined. The influence of diffusive layer thickness (0.515-2.015 mm), deployment time (3-168 h), and important environmental conditions-pH (3.02-9.45), ionic strength (0.0001-0.5 M), and dissolved organic matter (0-20 mg L-1)-were evaluated. The capacity of XAD, HLB, and MCX gels for binding all the test pharmaceuticals was ∼335 μg per disc, meaning that DGT could theoretically be deployed for over 30 months if there are no competitive effects or confounding factors. The uptake kinetics of psychiatric pharmaceuticals onto MCX gel were much faster than those onto XAD and HLB gels in the first hour. DGT measured concentrations of test pharmaceuticals at two sample points in a river (over 6 days) were comparable to those obtained by grab sampling. This study demonstrates the accuracy and reliability of DGT for measuring psychiatric pharmaceuticals across a wide range of freshwater conditions found in the natural environment.

Experimental Saltwater Intrusion Drives Rapid Soil Elevation and Carbon Loss in Freshwater and Brackish Everglades Marshes

Increasing rates of sea-level rise (SLR) threaten to submerge coastal wetlands unless they increase soil elevation at similar pace, often by storing soil organic carbon (OC). Coastal wetlands face increasing salinity, marine-derived nutrients, and inundation depths from increasing rates of SLR. To quantify the effects of SLR on soil OC stocks and fluxes and elevation change, we conducted two mesocosm experiments using the foundation species sawgrass (Cladium jamaicense) and organic soils from freshwater and brackish Florida Everglades marshes for 1 year. In freshwater mesocosms, we compared ambient and elevated salinity (fresh, 9 ppt) and phosphorus (ambient, + 1 g P m−2 year−1) treatments with a 2 × 2 factorial design. Salinity addition reduced root biomass (48%), driving 2.8 ± 0.3 cm year−1 of elevation loss, while soil elevation was maintained in freshwater conditions. Added P increased root productivity (134%) but also increased breakdown rates (k) of roots (31%) and leaves (42%) with no effect on root biomass or soil elevation. In brackish mesocosms, we compared ambient and elevated salinity (10, 19 ppt) and inundated and exposed conditions (water level 5-cm below and 4-cm above soil). Elevated salinity decreased root productivity (70%) and root biomass (37%) and increased k in litter (33%) and surface roots (11%), whereas inundation decreased subsurface root k (10%). All brackish marshes lost elevation at similar rates (0.6 ± 0.2 cm year−1). In conclusion, saltwater intrusion in freshwater and brackish wetlands may reduce net OC storage and increase vulnerability to SLR despite inundation or marine P supplies.

Climate-driven biophysical changes in feeding and breeding environments explain the decline of southernmost European Atlantic salmon populations

The consistency of the global declining trend of Atlantic salmon (Salmo salar) populations suggests that climate-driven reduced survival and growth at sea are the main driving factors. The southernmost populations have experienced the greatest declines, consistent with harsher conditions in natal fresh waters. We analyzed temporal trends in Spanish Atlantic salmon, important food organisms at sea, and climatic variables in the breeding (fresh water) and feeding (marine) salmon areas from 1950 onwards to elucidate drivers of declining patterns. Salmon abundance dropped abruptly in 1970–1971, plausibly linked to widespread overfishing coincident with incipient changes in the marine food webs and freshwater hydrology. A major regime shift in biophysical conditions throughout the North Atlantic salmon feeding grounds occurred in 1986–1987, driven by the concurrence of an abrupt acceleration in the anthropogenic warming trend and the warm phase of the Atlantic Multidecadal Oscillation. This regime shift may be the proximate cause of the collapse of Spanish salmon observed in 1988–1989, which kept declining in parallel to trends of ever-increasing ocean and freshwater temperatures, decreasing river flows, and poorer marine trophic conditions.

Applying the umbrella index across aquatic insect taxon sets for freshwater assessment

Abstract Biological surrogates in conservation biology are valuable for rapid biodiversity and environmental surveys, and as an early warning of potential threats. However, these surrogates need to be simple and inexpensive to apply. The umbrella index was applied here to quantify the selection of surrogate species for biodiversity assessments, but requires interrogation for application in areas rich in threatened endemic species. Aquatic larvae of Ephemeroptera, Plecoptera and Trichoptera (EPT), as well as the adult Odonata, are all highly responsive to changes in freshwater condition. Using the umbrella index, we evaluated the performance of the surrogate species approach for aquatic insect conservation in a region (Greater Cape Floristic Region) with an exceptional level of rare and endemic species, across multiple rivers with different disturbance levels. Due to a lack of species level information, EPT taxa were calculated using morphospecies within families, and Odonata were identified to species level. The umbrella index identified eight EPT species and seven Odonata species as potential surrogates. Both these groups co-occurred with high percentages of their own overall groups (EPT surrogates for overall EPT, and Odonata surrogates for overall Odonata), as well as for the other group (EPT surrogates for overall Odonata, and Odonata surrogates for overall EPT). The index was surprisingly flexible, and performed well in an area with so many species of conservation concern, as well as across spatial scales greater than a single river, with varying degrees of disturbance. Both EPT and Odonata showed promise as potential biodiversity surrogates, and for future conservation planning. Ideally, conservationists should aim to use taxa that are easy to identify to species level, with known sensitivities to human disturbance. However, when this is not a possibility, the umbrella index is still applicable and accurate for morphospecies (family level sensitivities).

Fluid migrations at the Krasny Yar methane seep of Lake Baikal according to geochemical data

Sediments of the deep water Krasny Yar methane seep area of Lake Baikal contain channels of 1 cm in diameter and up to a depth of 150 cm that have a high water content and are characterized by higher oxidized and reduced conditions than the surrounding sediment. New data of lithological and geochemical studies, including the full anionic and cationic composition of pore waters, indicate that chemical flow at the sediment surface of the seep is heterogeneous in space with both areas of inflow of fluids and areas with outflow of fluids. We suggest that much of this flow is modulated by more complex hydrological processes that may include aqueous pumping driven by gas expulsion- and changes in the permeability of the conduits due to gas hydrate formation and dissociation. We discuss the seep output fluid chemistry and heat flow in relation to the above hydrological processes and propose a seep model where fluid and gas migrations act at different spatial scales partly favored by hydrate accumulation and the fresh water conditions of Lake Baikal.

Intraspecific facilitation explains the persistence of Phragmites australis in modified coastal wetlands

AbstractCoastal exploitation and human‐mediated modifications have markedly altered the community composition and functioning of coastal wetlands worldwide. Although recent work has shown that harnessing positive density‐dependent feedbacks can greatly enhance the recovery of habitat‐modifying species in degraded wetlands, the role of these intraspecific feedbacks in explaining the persistence of altered, unfavorable plant communities remains largely unexplored. Here, we experimentally tested whether intraspecific facilitation may explain the persistence of common reed (Phragmites australis) in human‐modified coastal wetlands. We performed a full‐factorial mesocosm experiment crossing low‐density pioneer versus high‐density established development stages with saline (20 psu) versus freshwater conditions. Results showed a clear shift in plant growth response from intraspecific competition under freshwater conditions to self‐facilitation in saline treatments. We identified two positive feedback mechanisms enabling the established treatment to overcome salinity stress: (1) Enhanced root oxygenation of the sediment at higher plant density decreased accumulation and intrusion of phytotoxic sulfide, and (2) density‐dependent rainwater infiltration into the soil lowered salinity in the dense root mat, preventing salt stress. Our study demonstrates that intraspecific facilitation can be an important factor in explaining the persistence of Phragmites australis in coastal wetlands. We emphasize the importance of integrating positive interactions in coastal restoration but argue that they should either be harnessed when restoring vegetation or broken when eradication of nontarget species is the management objective.

The Potential and Limitations of Diatoms as Environmental Indicators in Mid-Atlantic Coastal Wetlands

Diatoms have been successfully used as indicators of past and present environmental conditions in freshwater and marine habitats, but their diversity and indicative properties in microtidal coastal wetlands of temperate zone are relatively poorly studied. The goal of this study was to determine whether diatoms can be used as indicators of sea level and nutrient content in coastal wetlands of the mid-Atlantic region of the USA. Our exploratory analyses indicated that benthic and marsh soil diatom assemblages were jointly controlled by tidal elevation, salinity, sediment texture, and nutrient content, while the relative importance of these factors varied among datasets targeting different environmental gradients. The habitat type could be correctly inferred from diatom assemblage composition in 79% of samples. A diatom-based model developed for inferring sediment nitrogen content had an average accuracy of prediction of 12.5% of observed nitrogen range. Models for inferring tidal exposure from diatom assemblage data provided assessment with 11–16% accuracy as estimated by the bootstrapped root mean square errors of prediction, which is similar to the accuracy of models based on other microfossils. These results show that despite inherent challenges, such as tidal redistribution of diatom frustules across the intertidal zone, diatoms can be successfully used as an independent source of evidence in paleoreconstructions of sea-level change and nitrogen enrichment, as well as for monitoring current nutrient pollution in mid-Atlantic wetlands.